Painting
wall paintWall Paint
Paint coverage based on wall dimensions, minus doors and windows, plus number of coats and coverage rate.
How to Use the Wall Paint Calculator
Enter your wall perimeter and height in feet, the number of doors and windows to subtract, your number of coats, and your paint's coverage rate (350 sq ft per gallon is a common average). The calculator returns your paintable area and the gallons to buy.
How the Calculation Works
The calculator starts with the gross wall area (perimeter × height), then subtracts a standard allowance for each door (20 sq ft) and window (15 sq ft) to estimate the actual paintable surface. That area is multiplied by your number of coats and divided by your paint's coverage rate, then rounded up to the nearest quarter gallon.
Example Calculation
A room with a 60 ft perimeter, 9 ft walls, 2 doors, and 3 windows, painted with 2 coats at 350 sq ft/gal coverage: gross area = 60 × 9 = 540 sq ft. Deductions = (2 × 20) + (3 × 15) = 85 sq ft. Paintable area = 455 sq ft. Gallons = (455 × 2) ÷ 350 = 2.6, rounded up to 2.75 gallons.
Frequently Asked Questions
Why subtract a flat amount per door and window instead of measuring each one?
Standard interior doors and windows fall within a fairly predictable size range, so a flat per-opening deduction gives a fast, reasonably accurate estimate without measuring every opening individually. For a room with unusually large windows or French doors, you may want to manually adjust for it.
What paint coverage rate should I use?
350 sq ft per gallon is a common average for smooth walls with one coat, but coverage varies by paint brand, sheen, and wall texture — textured or unprimed walls typically need more paint. Check the coverage rate printed on your specific paint can.
How many coats do I need?
Two coats is standard for most repaints, especially with a color change. A single coat may be enough when painting the same or a very similar color over a well-prepared surface.